Mostly documenting for myself, but these are the steps it took to get quickly up to speed in macOS with php, composer, docker for development.

Disable blocking apps from the internet:

sudo spctl --master-disable

Now, install the applications that we want from known sources.

Download and install kitty - https://sw.kovidgoyal.net/kitty/binary.html

curl -L https://sw.kovidgoyal.net/kitty/installer.sh | sh /dev/stdin

Start a terminal window and run these commands (or paste them in)

# Install homebrew - https://brew.sh/ for up to date instructions.
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"

# Install composer
brew install composer

# Install latest php
brew install php

# Install docker and git
brew install docker-compose git git-flow

# Change the default memory limit for php or composer will barf, -1 means no limit
sed -Ei '' 's/(memory_limit = )[0-9]+M/\1-1/g' /usr/local/etc/php/7.4/php.ini 

# Add ssh keys
cd
mkdir .ssh
chmod 0700 .ssh
vim .ssh/id_rsa # paste key in, save, exit.
chmod 0600 .ssh/id_rsa
ssh-add -K
ssh-add -l # to confirm the key is loaded